To be honest, there are like 200 different side effects when it comes to these meds and if doctors were honest with their patients about them, the number of people taking them would decrease drastically. I don't get why they don't mention the sexual dysfunction at least, it affects more than half of the people who take these drugs and even people who aren't that familiar with those meds know about that specifically. Also I don't understand why they'd prescribe you Citalopram aka an SSRI for insomnia, there must be way better options out there with less risks, I know that doctors push these meds for everything (including stuff like IBS and chronic pain) but it'll never stop being weird to me.
(This is gonna be super long which I apologize for, I just tend to overexplain stuff especially when I'm asked about it, feel free to not reply to me, I'm simply offering it as information)
I'd say they started immediately and then worsened gradually. This started in Jan 2020. One hour after I took my first pill I got a straining feeling on the surface of my brain, as if something was physically prodding at it, it was unlike anything I had experienced in my life but I told myself that it was probably just a headache side effect. That was in the morning, then in the evening something weird happened, I remember standing in front of the mirror, looking at my face and it was as if reality was falling apart, the muscles on my face felt weird and a bit paralyzed, I couldn't move my tongue as I wanter, it became harder to speak, I couldn't think properly.
During basically the first 2-3 days I suddenly lost access to most of my memories and vocabulary, it was hard for me to form any thoughts and keep them in my heads, to visualize anything, to speak, I got depersonalization and derealization in the form of a thick fog, I felt extremely detached from everyone and deeply sedated, my emotions were severely blunted and my visual and auditory processing were really off, like for example days prior to that I'd listen to certain music and watch certain things and they'd make me cry, laugh, feel fuzzy inside etc. But after I started the meds I felt numb both in my body and in my head and I couldn't even properly process what I was seeing/hearing. Those were my most debilitating side effects but I also got all kinds of pain and burning throughout my body, pressure, anger issues, chills, disorientation, extreme fatigue etc pretty much anything you could think of.
As for the sexual dysfunction, I've never had much of a libido so that didn't change much but I felt something like a blockage in my genitals? Sorry if this is TMI, basically any orgasm would be way harder to achieve and wouldn't be nearly as intense. Doctor kept me on the meds for 9 months thinking they would work at some point or that I'd feel better but after even few weeks of living like that I started feeling like a complete shell of my former self, like my life had never even happened, I'd only deteoriate further and further, my brain felt like it was splitting apart, I tried to CTB twice during those 9 months because of it and long story short, even after I stopped taking the meds, my brain stayed the exact same and has only been falling apart more and more, it's been more than 3 years since then and I'm almost completely non-functional. I really hope that all of your side effects lift once your stop the meds and you don't experience much of a withdrawal.